The invention relates to a fuel injection system for internal combustion engines.
As general prior art in this field, European Patent Disclosure EP 0 299 337 and German Patent Disclosure DE 195 49 108.4 are citedxe2x80x94as examples.
In particular, the invention is based on a so-called common rail system (CR system). The special feature of such CR systems is that the requisite fuel quantity has to be brought by a high-pressure pump to a variable pressure that is dependent on the applicable engine operating state. The high-pressure pump is driven as a function of the engine rpm, which can be done by cam shaft drive, for instance. The possible feed quantity of the high-pressure pump is designed such that in every operating state, an excess quantity of fuel, that is, more than is needed by the rail for the desired pressure buildup, can be pumped.
It is known for the fuel to be metered to the rail on the basis of a pressure regulating valve that is disposed in the high-pressure region downstream of the high-pressure pump. By means of this pressure regulating valve, the high-pressure fuel stream is split, on the one hand in the direction of the rail to increase/maintain pressure, and on the other in the direction of the fuel tank. This latter fractional stream is the overflow quantity, which at the same time means an attendant loss of efficiency.
In the present state of the art in CR systems, high-pressure fuel is accordingly diverted by the pressure regulating valve. This leads to high fuel temperatures and poor efficiency. Furthermore, the wide fuel temperature range in operation with a pressure regulating valve, dictated by the temperature-dependent density, leads to fluctuating injection quantities, which can be only partially compensated for by way of a temperature compensation by means of a temperature sensor.
By means of the system according to the invention, for a CR system of the type in question, a fuel metering unit is created that is capable of metering exactly the desired fuel quantity in the applicable engine operating state to the high-pressure pump of the CR system. By this kind of exact metering, of the requisite fuel quantity to the high-pressure pump, the unnecessary fuel overflow quantities that occur in previous fuel injection system prior art are averted from the very outset. This leads to improved efficiency and thus to fuel economies.